Thinking outside the embryo

Since 2001, when a federal funding freeze crippled research into the use of human embryonic stem cells to treat a host of congenital and degenerative conditions, molecular biologists have searched for a viable alternative. Now, they may have found a way. By reprogramming adult skin cells, researchers have produced stem cells that bypass the political and ethical stumbling blocks. But all is not perfect. In recent studies, the cells produced tumors in mice.